In gravure printing, minute recesses (cells) are formed in a hollow and tubular cylinder to be processed based on plate-making information to produce a printing surface, and the cells are filled with ink so that the ink is transferred onto an object to be printed. In general gravure cylinders, a tubular iron or aluminum core (hollow roll) is used as a base, and a plurality of layers such as an underlying layer and a separation layer are formed on an outer peripheral surface of the base. On those layers, a copper plating layer or any other plating layer is formed. Then, cells are formed in the copper plating layer or any other plating layer by a laser exposure apparatus based on plate-making information, and then the resultant base is plated with chromium or any other substance for enhancing printing durability of the gravure cylinder. In this manner, plate making (production of a printing surface) is completed.
The applicant of the present application has already proposed a copper plating apparatus for a gravure cylinder, including a plating bath to be filled with a plating solution, chuck means for holding a long cylinder at both ends in a longitudinal direction so as to be rotated and energized, and accommodating the cylinder in the plating bath, and a pair of opposed insoluble electrodes which is vertically installed so as to face both side surfaces of the cylinder in the plating bath, and is supplied with a predetermined current, the pair of insoluble electrodes being brought close to both the side surfaces of the cylinder with a predetermined interval to perform plating on an outer peripheral surface of the cylinder, in which the insoluble electrode has a shape in which a lower part thereof is curved inward, and is capable of rotating about an upper end thereof, and in which a thickness of a plating layer on the outer peripheral surface of the cylinder is adjusted by controlling an interval of closeness to the cylinder (Patent Document 1).
In the plating apparatus to be used in the manufacture of a gravure cylinder, the hollow and tubular cylinder to be processed serves as a cathode, whereas each of the insoluble electrodes serves as an anode. In recent years, the cylinder to be processed has been upsized, and hence the current density is increased in the prior art insoluble electrodes as disclosed in Patent Document 1, thereby causing a problem that the burden on the insoluble electrodes becomes significant. The significant burden on the insoluble electrodes causes a problem that platinum or any other substance used in the insoluble electrodes are consumed rapidly.
In the prior art insoluble electrodes as disclosed in Patent Document 1, when chromium plating is performed, impurities such as trivalent chromium are generated, thereby requiring work of removing the impurities. As a result, there is a challenge to minimize the generation rate of the impurities.